Interpretive Summary: Certain types of blue-green algae produce musty compounds that cause the muddy off-flavor in farm-raised channel catfish. The commercial product SeaKleen®, a natural compound used to treat ballast water from ships, was tested inside fiberglass enclosures placed in catfish ponds to determine its potential for controlling a type of musty blue-green algae prevalent in west Mississippi. Results found that SeaKleen® is effective in reducing the abundance of musty blue-green algae and the musty compound in catfish pond water.

Technical Abstract:
The cyanobacterium (blue-green alga) Oscillatoria perornata is the major cause of musty off-flavor in farm-raised channel catfish (Ictalurus punctatus) in west Mississippi. Currently, the only federally approved compounds for use as selective algicides in catfish aquaculture ponds in the southeastern United States are the herbicide diuron and copper-based products (e.g., copper sulfate). Due to environmental issues and the broad-spectrum toxicity of these synthetic algicides towards non-target organisms, there is a need for environmentally safe algicides for controlling O. perornata in catfish ponds. Laboratory bioassay screening of the natural product SeaKleen , a quinone-based biocide used to treat ballast water from ships, found that it is selectively toxic towards O. perornata compared to the green alga Selenastrum capricornutum. Subsequently, efficacy testing of SeaKleen was performed using limnocorrals placed in catfish aquaculture ponds containing O. perornata blooms. Two studies were performed: a dose-response study and a single effective-concentration study. For both studies, water samples were removed from within limnocorrals before and after application of SeaKleen to water contained within the enclosures. These water samples were monitored for levels of the musty off-flavor compound 2-methylisoborneol (MIB), chlorophyll a levels, and phytoplankton community structure. Results from both studies found that approximately 1.3 mg/L SeaKleen was effective in significantly reducing levels of chlorophyll a and MIB compared to controls. In addition, the abundance of O. perornata and other predominant species of filamentous cyanobacteria were significantly reduced compared to controls. Green algae and diatoms were not significantly affected. Additional studies are needed to determine the potential of SeaKleen as a selective algicide in commercial catfish aquaculture.